A mixture of 1-(2-fluoro-5-iodophenyl)-5-methoxy-4-oxo-1,4-dihydropyridazine-3-carboxylic acid (9.96 g, 25.5 mmol) and CDI (4.55 g, 28.1 mmol) in THF (200 mL) was heated to 40° C. for 30 min and 50° C. for 90 min. To the mixture was added DMF (20 mL). The mixture was stirred at 50° C. for 70 min. To the solution were added N,O-dimethylhydroxylamine hydrochloride (3.74 g, 38.3 mmol) and i-Pr2NEt (6.67 mL, 38.3 mmol) at room temperature. The solution was stirred at room temperature for 16 h. The mixture was concentrated in vacuo, diluted with water and 1 M HCl aqueous solution, extracted with EtOAc, washed with saturated NaHCO3 aqueous solution, dried over Na2SO4, filtered, concentrated in vacuo and purified by column chromatography on silica gel (hexane/EtOAc=20/80 to 0/100 and EtOAc/MeOH=100/0 to 0/100) and triturated with MeOH/EtOH/hexane to yield the title compound (9.11 g, 82% yield) as a pale yellow solid: 1H NMR (DMSO-d6, 300 MHz): δ ppm 3.24 (3H, s), 3.56 (3H, s), 3.80 (3H, s), 7.36 (1H, dd, J=10.6, 8.7 Hz), 7.93 (1H, ddd, J=8.7, 4.5, 2.3 Hz), 8.12 (1H, dd, J=7.4, 2.1 Hz), 8.53 (1H, s).
